In the manufacture of semiconductor devices photolithographic techniques are used to reproduce the image of a reticle onto a photosensitive resist covered semiconductor wafer. The reticle contains patterns that are imaged onto the photosensitive resist covered wafer. After a series of exposures and subsequent processing, a semiconductor device containing a circuit pattern thereon is manufactured. An illumination system is used to provide a flux of electromagnetic radiation for the projection of the image of the reticle onto a semiconductor wafer. The image of the reticle is formed by an optical projection system that collects the electromagnetic radiation after passing through the reticle and projects the image of the reticle onto the photosensitive resist covered semiconductor wafer. As semiconductor device manufacturing technology advances, there are ever increasing demands on each component of the photolithography system used to manufacture the semiconductor devices. This includes the illumination system used to illuminate the reticle. There are many prior illumination systems that enhance uniformity of illumination and minimize loss of light. One such illumination system is disclosed in U.S. Pat. No. 5,300,971 entitled "Projection Exposure Apparatus" issuing to Kudo on Apr. 5, 1994, which is herein incorporated by reference. Therein disclosed is an illumination system having a pulsed light source with a rotating deflecting prism used to direct the pulsed light to a fly's eye lens separated from the optical axis. A condenser is then used to condense the light from the fly's eye lens for illuminating a reticle. Another illumination system is disclosed in U.S. Pat. No. 5,296,892 entitled "Illuminating Apparatus and Projection Exposure Apparatus Provided With Such Illumination Apparatus" issuing to Mori on Mar. 22, 1994, which is herein incorporated by reference. Therein disclosed is an illumination system having an optical integrator or a fly's eye lens positioned before a condenser. The optical integrator or a fly's eye lens is designed to be replaceable so that the numerical aperture on the emission side of the illumination system can be varied. Another illumination system is disclosed in U.S. Pat. No. 5,245,384 entitled "Illuminating Optical Apparatus and Exposure Apparatus Having The Same" issuing to Mori on Sep. 14, 1993, which is herein incorporated by reference. Therein disclosed is an illumination system having an afocal zoom optical system placed before an optical integrator or fly's eye lens to vary the size of a plurality of secondary light sources. Yet another illumination system is disclosed in U.S. Pat. No. 5,237,367 entitled "Illuminating Optical System and Exposure Apparatus Utilizing The Same" issuing to Kudo on Aug. 17, 1993, which is herein incorporated by reference. Therein disclosed is an illumination system having a first optical integrator or fly's eye lens and a first condenser followed by a second optical integrator or fly's eye lens and a second condenser. The second condenser then provides illumination to a reticle. Either the first optical integrator or fly's eye lens and the first condenser have a variable focal length. A further illumination system is disclosed in U.S. Pat. No. 4,939,630 entitled "Illumination Optical Apparatus" issuing to Kikuchi et al on Jul. 3, 1990, which is herein incorporated by reference. Therein disclosed is an illumination system having a first optical integrator or means for forming a plurality of light source images followed by an optical system containing a second optical integrator or tertiary light source forming means followed by a condenser which directs illumination onto a reticle. A further illumination system is disclosed in U.S. Pat. No. 5,534,970 issuing to Nakashima et al on Jul. 9, 1996, which is herein incorporated by reference. Therein disclosed is an illumination system that uses a scanning pivot mirror to scan interference fringes to obtain desired illumination in a scanning exposure apparatus. Additionally, moving diffusers and other well established techniques have been used in the past in an effort to obtain more desirable illumination properties.
While many of these prior illumination systems have provided improved illumination for their particular application, there is still a need to provide an illumination system that can be easily manufactured and provides uniform illumination and eliminates or reduces pattern noise effects that may occur in these prior illumination systems when illumination sources that have coherence properties, such as a laser, are used in a scanning lithography system.